The oxygen sensitive and membrane bound diol dehydratase from Clostridium glycolicum was solubilized from its matrix by sonication of crude membrane preparations anaerobically in 0.1 M CHES buffer, pH 8.5 or 9.0, containing 2 mM dithiothreitol. Treatment with organic solvents, a variety of ionic and nonionic detergents, high ionic strength, or phospholipase A did not solubilize any diol dehydratase activity. Addition of 30% dimethylsulfoxide and 0.15 mg/ml of lysophosphatidylcholine to the CHES buffer before sonication markedly increased recovery of enzyme activity. Up to 45% of the activity could be recovered after centrifugation for 1 h at 105,000 x g. This solubilization method was also shown to work for the membrane bound formate dehydrogenase from E. coli. More than 95% of the activity was recovered in the supernatant after sonication and centrifugation.